Moparts Tech Archive

Big Block

516/906/452 head info...revisited

this is probably a little out of sync with some of the guys asking
questions about some of the various OE BB heads, but its the first
chance ive had to go through my notes and get a a few numbers together
for a little comparison chart of the flow characteristics in a few
basic stages of prep.

this info had been posted before when i did the original test
series, but some of it got lost or deleted when the tech archives got
revamped.

in any case, here is a representation of what you can expect from the different heads.
all tests and work were performed by myself, and all tests done on
the same bench, so the numbers are definately "apples to apples".

from a practical standpoint there are 3 common non-MW head designs.
-the 516 which has the poorer ports and closed chamber. this head
has intake and exhaust runners slightly different than any of the heads
made after them.

-the 906/915 heads are basically the same with the exception of the 915 being closed chamber.
these heads have the "tall" short turn, and when reworked correctly
should provide a slight edge in power over the other non-MW heads,
especially when using cams with .550 or less lift and moderate porting.
-the 346/902/452 heads are what was available after 1970, and came
on pretty much everything from 440 6bbl's to 400 2bbl's. from a
porting/power perspective, they are all the same and can be mixed and
matched with no problem.

the flow numbers are for 3 levels of prep. OE, a competition valve job, and then a competition valve job with the bowls blended.

as you can see, in this configuration there isnt a whole bunch of
difference between any of them in "peak flow", however the 906 has the
most area under the curve, and would make the most power.
from .300 thru .450 lift the 906 head averages between 15 and 20cfm better than the 516.
this is a pretty big difference in flow, right in the range where the piston is pulling the intake charge into the cylinder.

this particular 516, which had never had any valve jobs other than
OEM had an 84cc chamber volume, so it wouldnt have given much of a CR
increase over an open chamber head.

okay, here are a few examples of what i typically see from home ported BB Mopar heads.
its these kinds of results that are the reasoning behind why MP
says not to try and rework the short turn when you use their porting
templates.
for sure, if the short turn doesnt get reworked the amount of flow
you will gain is limited. but at the same time....you wont make the
heads flow any worse either.
these examples are a mix of home ported and work done by what i
imagine are some local shops near where the owners of the heads lived.

the first is a home ported 906 head with stock 2.08/1.74 valves. it
had a decent looking valve job with back cut valves, but the port work
was obviously not "professional" looking(not that how they look matters
to the flow bench).
these heads had the bowls opened up a bit too much, and just
enough material removed from the short turn to be a problem. they
either should have had less removed, or more removed(and then
reshaped).
the exhaust ports had the floors lowered way too much, and the port openings were HUGE.

so, better than unported, but still leaving a lot on the table, and
way too much material removed from the ports for the amount of gain.

next we have a 452 head ported by a guy i know in NY. these had a fair looking valve job but no back cutting.
on both intake and exhaust the entire port had been
reworked...and both were quite large....with the exhaust taking on that ever so popular HUGE look.
these had no polishing done what so ever.

pretty good numbers up top compared to stock...but its a pretty BIG port.
also, he was running a .460ish lift short duration cam, so the weak
low lift numbers and big ports arent doing much to much to enhance
velocity any.

this next one is from a set of 906's with 2.14/1.81 stainless valves.
nice looking valve seat work, but home ported after the fact by the looks of it.
no back cut, and the bowl was opened right up to the bottom of the
45 deg seat angle....a sure fire way to kill the low lift flow
capabilites of the bigger valve.
i tested 2 cylinders on this head...and this IS the better of the two.

at least this one didnt have the huge exhaust port opening, and you
can see that the larger exhaust bowl diameter starts to work at high
lifts, although the overall balance of the exhaust port isnt that great
considering it does have the 1.81 valve.

these next two were done by people who are supposed to know what they are doing.
one is so-so, the other is a joke.

first the so-so one. this is a 452 head with 2.08/1.74 valves.
it has a nice looking Serdi type valve job with back cut valves.
the port work looked pretty nice, but appeared to be more show and shine than metal removal.
they didnt really hurt anything, they just didnt really get much for the time they spent sanding on the runner walls.
pretty much the entire port had been polished, and the guide bosses had been streamlined as well.
they "looked" good.

they just took a bit too much off what little height there is to
the short turn on the intake side, and didnt quite get the seat blended
into the floor of the exhaust port which is why the exhaust flow got
worse at high lifts.

this last one i was told had been done by a shop that had a decent
reputation where this guy was from for doing Mopars....but i wouldnt be
surpised if he actually did the porting himself, or had a friend do it.
it looked pretty bad...and didnt work very well either.
this is a 906 head with 2.08/1.74 valves with a poor looking valve job and no back cut on the valves.

despite the exhaust port opening once again being HUGE(and quite ugly), the exhaust flow was awful.
the main reason for this was the installation of a hardened exhaust seat after the porting had been done...and it wasnt
blended back into the runner, leaving a BIG step where the seat meets the port.

keep in mind all of these examples have MUCH more work done to them than the ports listed in the previous post
that were "bowl blended".
it takes me about 15-20mins per CYLINDER(1-1.5 hrs per head) do get to that point.

all those numbers in the first post are using OE valves, 2.08/1.74 with a back cut for the last two configurations.

let me "define" what the various stages of rework are, in my view:

-competition valve, this is machining the seats with a 3 angle cutter for the intake, and a 2 angle into a radius
for the exhaust. the oe valves were back cut.

-bowl blend, this is just what the term implies.
blend the the casting into the machined part of the bowl.
on the 516, and 346/902/452 heads, since there isnt any short side
"radius" to speak of, a slight radius is applied where the bowl cutter
meets the floor. this is about 15-20mins of work per cylinder, on
pretty much any BB Mopar head.

-stage I-open pushrod pinch to 1.020, open bowls a little more than
a bowl blend, minor guide streamlining, more short turn work on both
intake and exhaust.
on the 516/346/902/452 heads, this is about 40mins per cylinder.
on the 906/915, its about another 10-15mins per cylinder to rework the
intake short turn.
the intake short turn on the 906/915 head is the "make it or break
it" area of the port. if its correctly shaped it will flow well and
make good power. if its done poorly you'll make less power and have
less flow.

for people doing their own porting without the aid of a flow bench,
the 346/902/452 head is a better choice since the general layout of the
port floor is more forgiving to having the shape be not quite right.

i cant seem to find my notes at the moment for the 'stage I' level
of prep to the 452 type head with the std sized valves.....but i'll
post those numbers when i find them.

as for the 516 and 906, here is how they compare with stage I prep and the OE 1.74/2.08 valves with a back cut.

at this point the 906 head is showing 533hp worth of flow at .550
lift, and has a 71.2% intake to exhaust ratio. on a properly built 440
bracket motor, 530+hp would easily be attained with heads that flowed
these numbers.

well....i couldnt find my notes for the 452 head, but i have a few
"test" heads laying around, so i did a "stage I" job to a 902 head with
the std valve size.
here are the results for from that porting, plus a competition valve job, and back cut OE 2.08 valve.

i timed myself on this one, and it took about 40mins for just this intake port.
to get an exhaust port to stage I takes about 15mins, so this is
roughly an hour per cylinder, not 40mins as i mentioned in the previous
post.

i didnt bother doing the exhaust port since all the exhaust ports from 1968 and up are pretty much the same.
i have run across a few 452 heads however that have had a fair
amount of additional material on the floor of the exhaust port than the
other heads, and although it does take a little more time to get those
ports working right, they do seem to be a bit better in the end.
not all the 452's are like that...but its pretty obvious if they
have the added material or not when youre looking into the bowl with
the valve removed.